The present invention relates generally to inkjet printers, and more particularly to an ink jet print head cartridge assembly adapted for shipping and installation with reduced leakage.
Ink jet type printers typically employ a pen body that is moved in a transverse fashion across a print media. Contemporary disposable ink pen bodies typically include a self-contained ink container, a print head supporting a plurality of ink jet nozzles in combination with the ink reservoir, and a plurality of external electrical contacts for connecting the ink jet nozzles to driver circuitry.
U.S. Pat. No. 5,686,947, which issued to Murray et al. on Nov. 11, 1997, discloses an ink jet printer which provides a continuous volume of ink to a pen body from a large, refillable ink reservoir permanently mounted within the ink jet printer. Flexible tubing, also permanently mounted within the inkjet printer, connects the reservoir to the pen body.
Even with the possibility of replenishment of the ink container within a disposable ink jet pen body, there eventually comes a time when the pen body must be replaced. Therefore, there is a substantial need to supply the market with replacement pen bodies. Leakage of ink from pen bodies during shipping and installation has been a problem in the industry. Consequently, replacement pen bodies have been shipped with xe2x80x9cbreathingxe2x80x9d caps so that the pressure inside the pen bodies equal to atmospheric pressure during shipping to deal with the elevation and temperature changes. The breathing cap has a long needle to reach to the central region of a cartridge cavity, and the ink level in the cavity must be low enough to prevent the tip of the cap needle touching the ink at all possible orientations of the pen body. As consequence, a prior art pen body is shipped with less than desired amount of ink in it. Even pen bodies equipped with breathing caps have been found to leak ink from the cap due to vibration during shipping; and installation of pen bodies with breathing caps can be messy, as ink can leak from the ink inlet or from the nozzles during the installation process.
The most likely path of ink leakage during shipping is via the nozzles on the jet plate. Nozzle plates are commonly covered by tape that relies either on a thin layer of adhesive or on electrical static to stick to the nozzle plate. The adhesion or static force attaching tape over a nozzle plate is able to withstand only a predetermined pressure differential between the pressure inside the nozzles and the outside ambient pressure. If the internal pressure increases, the pressure differential across the tape increases. The pressure differential across tape can also be affected by the change of atmospheric pressure. When the pressure differential across tape increases to the point at which the tape is not able to stand the pressure differential, ink forces the tape to separate from the nozzle plate, and ink leakage occurs.
The internal pressure P can be affected by many factors during shipping and during storage in a warehouse at a customer site. For example, a cartridge housing can be distorted for different reasons to cause its volume, and the internal pressure, to change. However, the biggest factor affecting the internal pressure is temperature. Temperature can change dramatically during shipping and storage. High temperature can be experienced in non-air-conditioned trucks and warehouses on hot days. Cold temperature can occur in a cargo airplane or in a warehouse at a cold location in winter. When a pen body is factory filled with ink, an initial internal pressure is applied and ink container is sealed off. During shipping and storage, when temperature increases, the internal pressure increases.
The atmospheric pressure is primarily affected by altitude. A change of altitude can be experienced by a cartridge assembly in a cargo airplane or when the cartridge assembly is transported to a location having a different elevation. At sea level, atmospheric pressure is 29.92 inches Hg. When altitude reaches 10,000 ft above sea level, atmospheric pressure decreases to 20.58 inches Hg. A pressurized cargo airplane typically allows pressure in the cargo chamber to decrease to as much as 11 inch Hg gage below the atmospheric pressure at sea level. When atmospheric pressure decreases to less than the internal pressure in an ink chamber, there is a danger for ink leaking to occur.
According to a feature of the present invention, cartridge assemblies are provided for shipping with the internal pressure of their ink containers set during assembly at a reduced level at least 2 inches Hg gage below atmospheric pressure at sea level to avoid leaking during shipping. Preferably, the ink containers have an internal pressure set at least 9 inches Hg gage below atmospheric pressure at sea level.